Modeling Friction on a Joint in Inspire Motion and Avoiding Redundant Constraints
Altair EmployeeBy default, in Inspire Motion, joints are treated as “Flexible” for the purpose of avoiding redundant constraints. If there is a need to include friction with a joint, the joint State must be set to “Active” and the joint Behavior must be set to “Rigid”. Depending on how the model is defined, when the joints are switched to Rigid, redundant constraints may result. Although not discussed here, there are ways to check for redundant constraints.
If there are redundancies, a new intermediate part can be created in-place at the joint location using normal Inspire Geometry capabilities. This new part is then used together with the original bodies in a new and slightly different setup arrangement that creates a non-redundant connection.
Essentially, adding the intermediate part and connecting with a Locked/Flexible takes a situation where there are two bodies connected with two joints and models it where there are two bodies connected with one joint, so there cannot be redundant constraints. The following document details the procedure for this. Keep in mind that this is not the only way this concept can be implemented, but is probably the simplest and fastest.
See attached document detailing this procedure.
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Thanks Scott for showing us this system and always providing outstanding customer service!
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With the 2021 release of Inspire you now have the option to set your joint(s) to 'Virtual'. This is another way to avoid redundant constraints and still be able to apply friction to a joint. Instead of blindly making all joints 'virtual' you might want to try using it on a case-by-case basis, in other words just use 'Virtual' on the specific joint that you will be enabling friction on. BTW, if you use the 'Virtual' joint option and your model starts to diverge during solution, you may have more success changing your Model Units to MKS.
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